Assessment of Degradation on The Interface of Concretes Cast at Different Times Subjected to Cyclic Shear Loading in Dry and Moist Condition

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Understanding the nature of shear transfer across an interface between old and new concrete is essential since the formation of this joint compromises the shear resistance capacity of a member as compared to a monolithically cast concrete. This kind of interfaces can be encountered in different areas of engineering. For instance, in various strengthening and repair works, when structural members cannot be cast at once due to work interruptions, when the construction method is a mixture of pre-casting and casting in place, rigid pavement construction and so on. In this paper, the degradation nature of the type of interface mentioned above is studied for cyclic shear loading in a dry and moist condition. Nine push-off specimens were cast on the experimental program. Three specimens were cast monolithically and tested in a dry condition while the others were made to have an interface. The surface of the substrate concrete was left as cast without any roughening. Three specimens were tested in a dry condition while the other three were tested in a moist condition. The specimens were tested while submerged in water in a tanker specially made for the test. Monotonic and one directional cyclic load at varying amplitude was considered for each set of specimens. A novel instrumentation scheme to measure the deformation at the interface was used. Three strain gauges were placed on each side of the interface in three different directions from which shear strain was calculated. This setup was used due to the rigid behavior of the interface before de-bonding occurs. The experimental program indicated that the presence of water pronouncedly accelerated the degradation of the interface for cyclic loading. A solid conclusion could not be made on the difference of degradation nature of concrete with and without an interface introduced with the limited number of specimens tested. The existence of a joint at the interface seemed to drastically reduce the shear transfer capacity for monotonic loading condition. A reduction of capacity up to 36.6% was observed. A model of the specimen with and without an interface was simulated on a nonlinear finite element analysis program DuCOM-COM3 for monotonic loading. The ultimate load was captured in a fair proximity with the available interface model.



Concretes Cast, Cyclic Shear Loading, Degradation